Project Abstract Road to discovery for Combination Probiotic Strain: BB-12 with LGG in treating autism spectrum disorders Stomach problems are common in children with autism. The proposed research project will study children with autism spectrum disorders (ASD), 4-15 years of age, who are complaining of recurring gastrointestinal (GI) symptoms, such as abdominal pain, constipation, and vomiting. These gastrointestinal problems are often associated with abnormal behavior, such as irritability. Our group is planning to test if at two different doses of a probiotic (defined as a bacterial product which when consumed in adequate quantity improves health) can benefit these children with GI symptoms. Oral doses of the probiotic we have selected (Lactobacillus rhamnosus GG and Bifidobacterium lactis BB-12, BB-12+LGG) to be tested are: a straw with 2 billion colony forming units (CFUs), a straw with 10 billion CFUs, and a placebo straw. We plan to enroll 70 eligible subjects with confirmed ASD and randomize them to placebo, low dose, and high dose of BB-12+LGG once daily at 1:2:2 ratio. The probiotic, to be added to food, may improve abdominal complaints which we hypothesize may produce changes in autistic behaviors that accompany these GI symptoms. Even though probiotics are widely available, the U.S. Food and Drug Administration requires that we demonstrate that this particular combination probiotic is safe in children before we can undertake a large multi-center trial to see if BB-12+LGG is effective at different doses in children with ASD. Based on previous trials in adults and adolescents, we expect no serious side effects from the use of BB-12+LGG. There will be 4 visits over 90 days. We expect to see a trend toward improvement of autistic behavior and GI symptoms by the end of the 56 days of treatment with BB-12+LGG at the highest dose. The pain and abnormal behaviors will be recorded using validated questionnaires. This study incorporates an Integrated Omics approach. Several blood and stool tests will be tested as potentially useful biomarkers of intestinal health in ASD, including a test of gut permeability (zonulin), a blood test for systemic inflammation (S100A9), and a stool test for inflammation (calprotectin). We will concomitantly measure bacterial communities in the stool (using 16S ribosomal DNA sequencing) and we will measure key metabolites in the blood and stool that have been proposed to contribute to GI symptoms in children with ASD (using high performance liquid chromatography). If an optimal dose of BB-12 + LGG is found to be safe and shows a signal toward improvement with respect to GI or autistic symptoms, we plan to study this probiotic in a larger, multi-center trial, using adaptive trial design.